Ask the store owner if you can put up a sign offering to pay five cents for each altoids box. That might convince folks to save 'em for you. Or you can discard your dignity and go hunting through your neighborhood's recycling.

(Note that there's nothing magical about the Altoids container. There are other candies/coughdrops which come in similar boxes. And other products which come in similar boxes, though plastic is more common than metal these days.)

But -- seriously -- even if you discard the contents, the box is pretty darned cheap.